electric fan

my electric fan is constantly turning off and on every 5 to 10 seconds. this is with the a/c and defrost off.sometimes it wont even stay on for 5 seconds. i just replaced the thermoatat the other day would this have anything to do with the sensor?

mine does that too, but I figure its not hurting anything.

actually, my fan stayed on once after the engine was off, so I pulled the relay to shut it off, but I'm not sure if thats even related, but maybe someone else here might have an idea.